Snipped from http://www.gnome.org/intro/findout.html:
"The GNOME project was born as an effort to create an entirely free desktop environment for free systems. From the start, the main objective of GNOME has been to provide a user friendly suite of applications and an easy-to-use desktop."
When the KDE project first started, the Qt libraries (http://www.trolltech.com/products/qt/index.html) were not yet free-as-in-speech. The GNOME project was founded to write a wholly free desktop environment. To this end, the GTK+ libraries (http://www.gtk.org) were used instead of Qt. GNOME is now at version 2.2, after a massive overhaul of GTK+ with version 2.0, which introduced a number of nice and pretty features, but which broke backward compatibility, necessitating rewrites of any programs that want to use the newest GTK+ libraries.
Both KDE and GNOME strive for standards compliance and interoperability, notably through the Free Desktop Project (http://www.freedesktop.org). One can run KDE applications under GNOME and vice versa, so it's pretty much a personal preference -- Gnome can be shinier, while KDE is generally more stable and mature. For comparison, take a look at Wim's screenshots of KDE 3 and these screenshots of Gnome 2.2: http://vhost.dulug.duke.edu/~louie/screenshots/2.2/
You can use this large GNOME Forum http://www.nabble.com/Gnome-f1226.html to find out what the GNOME developers and users are talking about. This forum currently archives the many GNOME projects' mailing lists into a forum for cross browsing and search. The forum host Nabble also have a Free Desktop Forum http://www.nabble.com/Free-Desktop-f1043.html